The present invention relates to a controller of a vacuum brake power booster for vehicles.
There is a power booster such as disclosed in JP A 11-129889. Further, JP w 11-505489 discloses a electro-mechanically controllable brake power booster irrespective of the intention of a driver, which has a function of opening/closing a valve mechanism, linking with a brake pedal operated by the driver and in addition thereto a function of opening/closing the valve mechanism, based on balance of electromagnetic force of a solenoid linked with the valve mechanism and spring force generated depending on displacement of the solenoid. The valve mechanism adjusts an air flow rate between a fixed pressure chamber and an operation pressure chamber of the brake power booster, causes a pressure difference between the fixed pressure chamber and the operation pressure chamber and applies pressure to a brake liquid in a master cylinder. The pressure is transported to a sleeve cylinder of each wheel and brakes the vehicle.
In such a brake power booster, when brake is effected irrespective of the intention of a driver (hereunder referred to as automatic brake), a flow rate of air passing through the valve mechanism being opened depends on an opening area of the valve mechanism determined according to balance of electromagnetic force of a solenoid, spring force, slide resistant force of a seal material and a difference between a atmospheric pressure and a pressure in the operation pressure chamber, and a pressure difference between the fixed pressure chamber and the operation pressure chamber or between the operation pressure chamber and atmospheric pressure. The air flow rate relates to the pressure difference between the fixed pressure chamber and the operation pressure chamber, and directly relates to a speed of pressure increase or pressure decrease in the master cylinder. For example, in the case where the automatic brake is operated at a negative pressure (for example, 350 hPa) in both the fixed pressure chamber and the operation pressure chamber, current is flowed into the solenoid to open the valve mechanism, air is flowed from the atmosphere into the operation pressure chamber and a pressure difference is caused between the fixed pressure chamber and the operation pressure chamber. When it reaches to a desired pressure, the current flow to the solenoid is stopped and the valve mechanism is closed. The pressure difference between the fixed pressure chamber and the operation pressure chamber is maintained while the valve mechanism is being closed, whereby the pressure in the master cylinder also is maintained. At this time, in the valve mechanism, the electromagnetic force caused by solenoid current, the spring force applied on the valve, force due to a difference between a pressure in the operation pressure chamber and an atmospheric pressure and a slide resistant force of the seal material partitioning the operation pressure chamber and the fixed pressure chamber are balanced. When the pressure in the master cylinder is further raised, current is flowed again to the solenoid to open the valve mechanism and causes air to flow into the operation pressure chamber. At this time, the pressure in the operation pressure chamber has become higher than when the valve mechanism was opened previously, and an inflow speed of air is slow even if the opening area of the valve mechanism is the same, whereby the rate of pressure increase in the master cylinder becomes slow. That is, a speed of increase or decrease of pressure in the master cylinder changes according to the pressure of the operation pressure chamber. However, from a viewpoint of a speed controller generating a pressure command in the master cylinder, the controller can be handled easier when a change in speed of increase or decrease of pressure in the master cylinder is smaller.
Further, in the case where the above-mentioned air is flowed into the operation pressure chamber, the slide resistant force of the seal material changes according to a change in coefficient of friction from a static friction coefficient to a dynamic friction coefficient. By the change in friction coefficient, the balance of the above-mentioned four forces is broken and the valve mechanism suddenly opens. In order to reduce the change in the slide resistant force of the seal material, a technique of current dither (DTER) exists, which periodically changes solenoid current so that the slide resistant force is always a slide resistant force in a region of a dynamic friction coefficient. By superimposing a dither (DTER) on the solenoid current, it is possible to open the valve mechanism more smoothly than when the dither is not superimposed. When closed, it is possible to close smoothly by applying a current dither in a similar manner. However, to superimpose the dither on the solenoid current means that the current always changes rapidly. Thereby, electromagnetic noises increase, which may be a cause that they make it unable for a driver to easily listen to radio broadcast, with the noises carried to the radio.
An object of the present invention is to provide a controller of a vacuum brake power booster in which the above-mentioned problems are solved and it is possible to effect pressure control without decrease in a speed of pressure increase or boost up which is caused by a change in an operation pressure chamber of the power booster.
The above-mentioned object is solved, in a controller of a vacuum brake power booster amplifying an input of a brake pedal and outputting to a brake device, by comprising control signal generating means generating a plurality of kinds of signals for controlling the power booster, and means for switching or selecting the plurality of signals on the basis of an input different from one of the brake pedal.
Particularly, a brake device comprises a brake power booster constructed by dividing a shell body inside into two, front and rear chambers by a center shell and dividing each of the two, front and rear chambers into a fixed pressure chamber and an operation pressure chamber by a front/rear power piston having a diaphragm, arranging, in at least a valve body supported by the rear power piston, a plunger connected to an input shaft extending from a brake pedal, a valve mechanism linked with the plunger and generating a pressure difference between the fixed pressure chamber and the operation pressure chamber and an annular solenoid case containing therein a solenoid controlling operation of the valve mechanism independently of movement of the plunger, thrusting each power piston by a pressure difference generated between the fixed pressure chamber and the operation pressure chamber, transmitting the thrust force to the output shaft through the solenoid case and transmitting a part of the reaction at that time to the input shaft through a reaction disk retained by the solenoid case and the plunger; a master cylinder connected to the input shaft; a pressure sensor measuring the pressure of liquid fully filling inside the master cylinder; a current source flowing current to the solenoid; and pressure controlling means for calculating one by one a current command value to be flowed to the solenoid, based on a pressure sensor value and a pressure command. In the above-mentioned pressure controlling means, a least 4 current commands, of high speed pressure increase, pressure increase, pressure retention and pressure decrease are calculated, any one of the above-mentioned 4 current commands is switched or selected to be a current command Ir. The 4 current commands Ir are optimized for pressure change. Particularly, for pressure increase for operating the brake device, a high speed pressure increase and an usual pressure increase, that is, 2 kinds of commands are provided, and a current command for the high speed pressure increase is set so that the area of opening of the valve mechanism is always maximum, and it is possible to make up a decrease in pressure increase speed due to the pressure of the operation pressure chamber described previously.
Further, the current command Ir includes current dither optimized to realize smoothness of the pressure change, the amplitude of the current dither changes depending on pressure command Pr and a value Pm of the pressure sensor. The amplitude of the current dither is made large when a difference between the pressure command and the value of the pressure sensor and made zero when the difference is small. That is, the amplitude of the current dither is made zero when the pressure control is managed well, and the current dither is made large when the difference between the pressure command and the value of the pressure sensor becomes large. Thereby, it becomes possible to control the amplitude of the current dither to be a necessary magnitude, and it is possible to reduce the electromagnetic noises.